Lake Bacalar (or Laguna de Bacalar) is a long and narrow lake in the state of Quintana Roo, Mexico. It is approximately 42 km long measured from north to south, and less than 2 km at its widest. The lake is renowned for its striking blue color and water clarity, partly the result of having a white limestone bottom. Like most bodies of water in the Yucatán peninsula, the lake is fed by underground rivers or cenotes.
On the lake's western shore is the village of Bacalar, population 11,084.
In November 2015, Mexico's federal environmental protection agency issued a pollution alert for Lake Bacalar as a result of illegal dumping and inadequate wastewater treatment.